1. Field of the Invention
The invention relates generally to devices and methods for deflation of an inflatable packer device in the event of a loss of power to the inflation pump or another emergency requiring a secondary method of deflation. In particular aspects, the invention also relates to inflatable packer assemblies that incorporate a deflate sub having a dumping chamber with an interior pressure that approximates atmospheric pressure.
2. Description of the Related Art
Inflatable packer assemblies are well known in the industry. These packer assemblies incorporate an inflatable packer element, or bladder, which is selectively inflated using a pump to flow fluid, such as borehole fluid, into the bladder. The packer element is ordinarily deflated by reversing the pump so that the fluid is flowed out of the bladder. A problem arises if there is an emergency wherein power is lost to the pump. The packer element cannot be deflated and, typically, the packer assembly must be detached from the tubing string. The tubing string is then removed from the borehole and the packer assembly subsequently removed using a fishing tool. This technique, while effective, is costly and time consuming. The well must be essentially shut down so that the tubing string can be removed and the fishing tool run in.
U.S. Pat. No. 5,297,633 issued to Snider et al. describes an inflatable packer assembly wherein a reciprocable fluid piston assembly is used to selectively inflate and deflate the packer. If the packer becomes stuck in the wellbore, the operator can pull up on the tubing string to shear a shear pin, thereby leaving the stuck packer in the well for later retrieval by a fishing tool. This solution for removing a stuck packer should be considered to be a last resort since it requires the well to be closed down, the sampling tool removed from the hole and a fishing device then run into the hole to retrieve the stuck packer. This is costly and time-consuming.
The prior art does teach the use of a bladder""s natural shape memory to urge fluid out of the bladder. U.S. Pat. No. 4,676,310 issued to Scherbatskoy et al., for example, describes a transporter device for moving a logging tool. The transporter device includes an expandable bladder that is filled with fluid to become inflated and engage a borehole wall. The fluid is provided from an expandable reservoir. In one construction, the bladder is of a resilient construction that will normally urge fluid to flow back into the expandable reservoir. In practice, however, this arrangement is practically useless since the expandable reservoir is subject to hydrostatic pressure that precludes effective evacuation of the bladder. Little or no flow of fluid can be expected. Furthermore, there is no positive control of deflation.
An example of this is found in U.S. Pat. No. 6,257,338 issued to Kilgore, which describes a tubing string with multiple inflatable packers. The packers are inflated and deflated using a coupling that is conveyed down inside the tubing string on coiled tubing. When deflated, the fluid from the packer flows into the interior of the tubing string. Thus, fluid within the packer element is expected to flow into an area that is under hydrostatic pressure and, if such pressure is sufficiently great, deflation will be unsuccessful.
The arrangements of the prior art demonstrate the absence of an acceptable emergency deflation mechanism. To the inventors"" knowledge, there are no conventional arrangements that provide a suitable mechanism for deflation of the packer element in the event of a loss of power to the fluid inflation pump or another such emergency.
There is a need to provide improved methods and devices for rapid and effective deflation of an inflatable packer. The present invention addresses the problems of the prior art.
The invention provides devices and methods that permit a packer element to be deflated in the event of an emergency wherein power to the inflating pump is lost. The invention also provides a backup procedure in the event that deflation of a packer element using conventional techniques is not successful. The devices and methods of the present invention, therefore, provide a more certain technique for deflation and removal of a packer assembly short of having to detach the packer assembly from the tubing string and fishing it out of the borehole with a separate tool. Thus, the invention offers a significant savings of time and money over the prior art.
In a described embodiment, a well sampling tool is described that incorporates an inflatable packer assembly having packer elements are selectively inflated by fluid pumped from the wellbore through an inflation tube into the packer elements. The packer assembly includes a deflation sub that houses the components of the emergency deflation mechanism. The deflation sub defines a dumping chamber that is at approximately atmospheric pressure. The dumping chamber has a capacity that will accept enough of the fluid contents of the inflated packer elements so that the packer elements become deflated enough to become disengaged from the borehole wall. Additionally, the deflation sub retains a portion of the inflation line for the packer elements and a means for separating the inflation line. In a currently preferred embodiment, the means for separating the inflation line includes a split rod arrangement wherein two reversibly interconnectable portions of the line may be axially separated from one another. To enable separation of the split rod, a hydraulic piston arrangement is formed within the deflation sub having a piston and surrounding piston housing. Shear pins or other frangible members are used to prevent premature movement of the piston and to provide a positive indication of movement of the piston.
To actuate the emergency deflation mechanism, an operator pulls up on the tubing string. The piston is then moved axially with respect to the housing, causing the split rod arrangement to separate the inflation line. Fluid from within the packer elements is then released into the dumping chamber to deflate the packer elements. Because the packer elements are subject to external hydrostatic pressure, the fluid contents will readily flow into the dumping chamber. In the unlikely event that the emergency deflation mechanism fails, the packer assembly may still be separated from the tubing string, in the conventional manner and later retrieved with a fishing tool.
The invention also has applicability to other packer arrangements and mechanical tools that utilize hydraulic fluid to be selectively set within a wellbore.